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Following an accident report from the MAIB published in MARCH report and translated in Afcan Infos 68 (May 2005), the Yara company which read the text on our site forwarded us informations concerning its process of treatment of the cleansing networks. Although, originally, the system is planned for a ground network, the accident reported by the MAIB, which has occurred onboard a ship, deserves that one puts the question about the means of strongly reducing the formation of H2S in the grey and black water circuits of a ship.

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Why is it necessary to fight against H2S?

Toxic process

When it is present at high concentrations, the hydrogen sulphide (H2S) paralyses the olfactory nerves, which makes it undetectable and therefore more dangerous. H2S can thus be at the origin of serious ocular, respiratory, even cerebral disorders. A short time exposure to strong H2S concentrations of (about 500 to 1000 ppm) generate respiratory paralysis quickly leading to death.

Effets néfastes sur la santé

	H2S (in ppm)		EFFECTS
	0.002 -0.2		OLFACTIVE THRESHOLD
	3 – 5		STRONG SMELL
	10		OPERATIONAL LIMIT OF EXPOSURE
	10 – 50		OCULAR IRRITATION
	50 – 100		SERIOUS OCULAR DISORDERS
	250		LOSS OF THE SMELL SENSE
	300 – 500		SERIOUS RESPIRATORY TROUBLES - MORTAL DANGER
	500 – 1000		SERIOUS DISORDERS OF THE CENTRAL NERVOUS SYSTEM, RESPIRATORY PARALYSIS
	1000		IMMEDIATE DEATH

The Ministry of Labour imposes the following standards:
Exposure Median value (VME) = 5 ppm - Exposure limit value (VLE) = 10 ppm

Expensive consequences
H2S corrodes the drainage systems. Indeed, H2S in contact with the walls of the collectors, turns into sulphuric acid which corrodes the concrete (and metals). The biochemical corrosion of materials gradually involves the degradation of the drain until it collapses.

Smelly process
H2S is smelt in weak concentrations (0,002 to 0,2 ppm) in a broad perimeter around the networks, the pumping stations and the purification plants. Its characteristic smell of rotted egg, particularly unpleasant, generates harmful effects for the residents. This generates a negative publicity with respect to the plants and their operators.

Disturbing process
The presence of dissolved sulphides can support under certain conditions the development of filamentous bacteria responsible for a reduction in the purification outputs.

Yara France proposes :

• the implementation of a solution of effective treatment, controlled and non dangerous.
• services of a specialised engineering team
• the realisation of a turnkey installation

The NUTRIOX® applies in:

• cleansing network
• pumping station
• purification plants
• paper manufactory, printing industry
• agribusiness industry

The NUTRIOX® is a product (classified) nondangerous. The NUTRIOX® does not form additional muds,
The NUTRIOX® does not colour water.
The NUTRIOX® process is found in , 200 sites in France and 1000 in Europe. Yara is certified Iso 9001 version 2000.

The durable elimination of H2S

How H2S is formed?

When the conditions of septicity are met, the waste water is found in phase known as of anaerobe.
In this phase, occurs the formation process of dissolved sulphides (S2-) and hydrogen sulphide (H2S).
The active bacterial populations in anaerobe are the fermentative bacteria and the sulfato-reducing bacteria. They use sulphates as energy source to degrade the organic matter and thus produce dissolved sulphides and H2S.

The calcium nitrate inhibits the formation of H2S

Introducing calcium nitrate in waste water completely inhibits the formation of dissolved sulphides and H2S.
The nitrate introduction will make it possible to maintain the effluents the state of anoxia (and not in anaerobe) in which the formation process of H2S is completely blocked.

Process NUTRIOX® :

The formation of H2S varies continuously, the calcium nitrate proportioning must thus be adapted. The NUTRIOX® , process is a controlled calcium nitrate injection. Proportioning is permanently optimised.

Due to the proportioning controllers especially developed by Yara, the quantity of calcium nitrate to be injected is permanently calculated and optimised. The process makes it possible at every moment to define the strictly necessary quantity of reagent to be injected. Indeed, our proportioning controllers use a dynamic model and allow to take into account the variations of the various parameters influencing the formation of H2S.

Thus the quantity of reagent used is completely consumed and allows the total abatement of H2S.

To diagnose:
Yara France proposes complete diagnostic studies in order to identify the sources of emissions of H2S, to quantify the emanations and to define the problems of network. The risks of toxicity, corrosion and emanations of bad smells are then evaluated.

To conceive and show:
Each case being specific, the company Yara France proposes the implementation of pilot treatments. These phases of tests make it possible to determine the treatment best adapted and to show the effectiveness of NUTRIOX® process over a given period.

To treat durably:
After feasibility study, the company Yara France achieves the treatment plant, which includes:

• storage unit
• the injection unit
• the proportioning controller

These units can be integrated in the existing systems of teleprocessing.

The teams of Yara France ensure an annual technical control and a verification of performance of the installation and will help customer for any evolution.

The training and the information of the operating personnel are ensured before the first start of the plant.

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Yara France :		100, rue Henri Barbusse - 92.751 Nanterre Cedex - phone: 01 55 69 96 00 - Fax: 01 55 69 98 56 - www.yara.fr
Southern agency:		Parc Aquatechnique lot B13 - 68, rue de Dublin - 34200 SETE - phone: 04 67 18 65 90 - fax: 04 67 18 65 91
Western agency:		BP 11 - 44550 Montoir de Bretagne phone: 02 40 17 16 37 - fax: 02 40 17 16 65
Northern/East agency:		100, rue Henri Barbusse - 92751 Nanterre phone : 01 55 69 96 02 - fax : 01 55 69 98 56
Technical centre:		Parc d’activité Secteur 2 - 60, rue de l’Industrie - 77176 Savigny le Temple

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